Conventional fluorescent lighting assemblies employ ballasts that are connected to opposite ends of fluorescent lamps. For preheat or rapid-start fluorescent lamps, the ballast is connected in series with the two pins and the filaments at opposite ends of the lamp when the starter switch is closed. When the starter switch is opened the ballast reactor produces a high voltage between filaments at opposite ends of the lamp striking an arc through the argon and mercury vapor in the lamp.
For an instant start fluorescent lamp, no starter switch is used. The circuit is arranged so that a high voltage will be impressed across the lamp when the lamp circuit is closed and the voltage across the lamp is reduced to its normal operating value as soon as conduction takes place and the lamp is started.
In each case the ballast is connected to the bases at both ends of the fluorescent lamp. At least one commercially available instant start ballast is capable of operating multiple lamps in which the ballast is connected only to the pins or electrodes on the ends of the multiple lamps. Interior pins on adjacent lamp bases are commoned. The MULTILITE MUL120 manufactured and sold by Electrofab, Ltd. is capable of energizing an eight foot instant start fluorescent lamp or two four foot instant start fluorescent lamps with adjacent pins on adjacent lamp bases commoned. However this ballast is used in conventional applications where the ballast is mounted between opposite ends of the lighting fixture.
For conventional ballasts used in overhead troffers or luminaires, the ballast or ballasts are mounted at the center of the troffer and attached to the top of the troffer. Wires extend from the ballast or ballasts to sockets located at opposite ends of the troffer. For a four lamp assembly, wires must be connected to sockets at both ends of the four lamps. When a defective ballast is replaced, often on a trial and error basis, these wires must be disconnected and reconnected. Installation and maintenance of conventional lighting assemblies is therefor time consuming and cost is added to the manufacture of the lighting assembly.
One approach to simplifying and therefore reducing the cost of ballast installation is disclosed in U.S. patent application Ser. No. 08/309,300 filed Sep. 20, 1994 (now U.S. Pat. No. 5,720,546), assigned to The Whitaker Corporation. An integral ballast that can be mounted at one end of a lighting assembly is disclosed in that application. However, a neutral wire must still be connected to the opposite end of the lighting assembly and this wiring must be completed during assembly of the lighting fixture.
U.S. Patent Application (Attorney's Docket No. 16834) entitled Fluorescent Lighting Assembly with Integral Ballast eliminates the need to wire sockets at both ends of a fluorescent lighting assembly to a ballast. The ballast subassemblies depicted as the preferred embodiment of that invention are however still intended to be used with standard troffers or pans that fill two panel sections of a standard suspended ceiling.
The large lighting troffers used with conventional suspended ceilings serve several purposes. They provide a mounting surface for the conventional ballast located along the top; ballast cover channels covering the ballasts can be mounted on the troffers; diffusers, lenses, louvers and baffels can be mounted on the troffers; and the troffers support lamp sockets and fluorescent lamps mounted therein. These sheet metal troffers also provide fire protection enclosure, electrical grounding and act as a heat sink for the ballasts and for the fluorescent lamps. However, these conventional troffers are quite large and bulky, making them difficult to install and costly to ship. For example, a standard troffer commonly used for four foot fluorescent lamps is approximately four feet long, two feet wide and four inches deep. Although these standard troffers are dimensioned to be supported by the T-bar frame of a conventional suspended ceiling, they are bulky and can require two installers to position the troffers in a suspended ceiling. To wire a fixture of this type, the power wiring and the flexible metal conduit must be attached to the troffer through an access opening normally before the troffer is installed. The wiring can then be connected to the ballast secured to the top of the troffer. The ballast can be attached to the troffer before it is mounted in the suspended ceiling, although this would add weight, further complicating installation of the troffer. Conventional ballasts could be attached to the top of the troffer after it is positioned in the suspended ceiling.
There have been several attempts to eliminate the relatively large and expensive fixtures, and troffers, that occupy one or more full panel openings in a suspended ceiling. U.S. Pat. No. 4,363,082 and U.S. Pat. No. 4,407,011 show lighting fixtures that are either mounted in narrower and therefore more numerous panels or fluorescent lighting fixtures that can be mounted in openings in larger frames that separate and support ceiling panels. However, neither of these approaches is suited for use with standard suspended ceilings that use T-Bars forming panel openings on a two foot by two foot matrix and provide openings of four feet by two feet for use with standard four foot fluorescent lamps.
One other fluorescent lighting approach attempts to simplify the lighting fixture by positioning a conventional ballast in a central housing and by cantilevering U-shaped fluorescent tubes from the central housing. U.S. Pat. No. 5,526,244, however, is intended for use in an overhead luminaire that is mounted below the ceiling.